##uniq - report or omit repeated lines, used with sort
uniq一般只和sort结合使用，很少单独使用
	-c, --count
			prefix lines by the number of occurrences
    -d 只显示重复的行

##tee - read from standard input and write to standard output and files.
	tee只会把正确的信息重定向到文件中，错误的不会，如下：
	[root@CH ~]# ls
	1.txt  3.txt  anaconda-ks.cfg  b.txt  date.sh         install.log      install.log.syslog  test
	2.txt  aa     a.txt            c.txt  ifcfg-eth0.bak  install.log.bak  paswd
	[root@CH ~]# ls 3.txt  5.txt | tee 1.txt
	ls: cannot access 5.txt: No such file or directory
	3.txt
	[root@CH ~]# cat 1.txt
	3.txt

##tr - translate or delete characters
	[root@CH ~]# echo 'adsljfl;adjfl'  | tr 'a-z' 'A-Z'
	ADSLJFL;ADJFL
	[root@CH ~]# echo 'adsljfl;adjfl'  | tr 'a-f' 'A-Z'	
	ADsljFl;ADjFl
	#下面的替换就是一一对应的
	[root@CH ~]# echo abcdefg | tr 'abcdefg' 'ABEFDG'
	ABEFDGG

	split - split a file into pieces
